Spanners are the most representative fastening tools for tightening or releasing a bolt or nut etc. operated by a leverage of the gripping lever in a shape of a stick. Generally, a spanner is constructed to have a gripping lever in a shape of a stick, and two jaws extending respectively from the lead end of the lever. When a bolt (or nut) is inserted in a gripping space formed between the two jaws, the bolt is tightened or released by rotating the lever while applying force to the lead end of the lever using the leverage exerted in proportion to the length of the lever.
At present, there are different kinds of spanners, such as a typical type of spanner having a fixed distal end between two jaws to be applicable to a bolt (or nut) of only one specification, a monkey spanner having a movable distal end between two jaws by relatively moving a jaw toward the other jaw to be applicable to a bolt of all specifications, and a ratchet spanner having a ratchet mechanism constructed to apply force only in one direction so as to be capable of tightening or releasing a bolt rapidly by the continuous operation of rotating the lever in one and other converse directions repeatedly in a state of gripping the bolt. Users selectively use the proper type of spanner depending on working conditions, but the ratchet spanner is most widely used for its convenience among these spanners.
However, if only a narrow gap is allowed for the operation of tightening a bolt where the ratchet spanner is not applicable due to the heavy thickness of its socket in spite of its convenience, then a user has to use a flat spanner. But, in a flat spanner, the user has to endure the inconvenience of repeatedly inserting the bolt in the jaws of the spanner after rotating the spanner a certain number of degrees, which has the problem of greatly decreasing efficiency.
To solve this problem, there has been suggested a spanner with a ratchet mechanism having a thin thickness and that can be operated without a socket, as disclosed in Korean Patent Laid-Open Publication Nos. 10-2000-0000449, 10-1999-0028347, and Korean Utility Model Registration Nos. 20-0243241 and 20-0261440.
However, these conventional spanners have a common problem in that their manufacturing is difficult due to the complex construction and structure of the ratchet mechanism installed for rotating in one direction. Moreover, the jaws for gripping the bolt have an overly large volume, therefore the spanner with a ratchet mechanism can't be used if only a narrow gap is allowed for the operation of tightening a bolt.
Considering these problems of conventional spanners with ratchet mechanisms, the applicant of the subject invention has also developed a spanner having a thin thickness as well as a simple construction and structure known as “an automatic spanner”, as disclosed in Korean Utility Model Registration No. 20-0309103.
This automatic spanner solves the above problem partly, but it has a problem in that the toggle bar extrudes beyond the outside surface of the jaw so that the width (the distance between the outside surfaces of the two jaws) becomes too large, therefore the automatic spanner can't be used when a narrow gap in width is allowed for the operation of tightening the bolt. Moreover, it is difficult to adjust the tension of the torsion spring supporting the toggle bar, so that the friction force of the toggle bar against the bolt can't be adjusted appropriately to working conditions, which frequently decreases working efficiency. Also, the automatic spanner has another problem in that the rear end of the toggle bar extrudes to the exterior so that it is easily broken by external impact, and the torsion spring supporting the toggle bar is exposed to the exterior, so that the tension spring may easily rust or break from external impact, thus shortening the durability of the spanner.